1. Field of the Invention
The present invention relates to an angle estimation method and a radar system, and more particularly, to an angle estimation method and a radar system capable of enhancing angle estimation accuracy.
2. Description of the Prior Art
Phase impulse radar systems are usually equipped with one transmit antenna and two receive antennas. The radar system estimates an angle/direction of arrival (DOA) of a target object via a time difference of signals received by the different receive antennas. Specifically, the radar system may generate the phase difference corresponding to the time difference of received signals from different antennas. Since the phase difference and the DOA of the target have a specific corresponding relationship, after the radar system obtains the phase difference of the received signals from different antennas, the radar system may compute the DOA of the target object. An accuracy of angle estimation depends on how the time difference between antennas is matched to a theoretical value. If the estimated angle is closer to the theoretical value, the estimation accuracy is higher. Otherwise, the estimated angle may have an error in different degree.
In practice, factors of affecting the time difference could be length/material of a path between antenna(s) and a backend signal processing apparatus, sampling time of the antennas, and medium of the radar wave emitted by the radar system toward the target object. The former two factors may be calibrated by proper design and compensated through a manufacturing process. The latter factor, which is the medium of the radar wave emitted by the radar system toward the target object, depends on the practical environment of the radar system. Take a vehicular radar system as an example, since the vehicle radar system is disposed within a bumper, a time difference would be affected by a curveness and a material of the bumper, and a phase ambiguity occurs. That is, different angles may correspond to a same phase difference, which may degrade an accuracy of DOA estimation.
To reduce angle estimation error brought by the phase ambiguity, the prior art enhance the accuracy of DOA estimation by including more antennas and increasing distance (s) between the antennas. However, including more antennas and increasing the distances between the antennas would enlarge the disposing space for the radar system, which is not good for the vehicular radar system. Therefore, how to enhance DOA estimation accuracy without enlarging the disposing area of the antennas within the radar system is a significant objective in the field.